fix: support latest Ghostty VT API in macOS build

[roodboi]

Summary

• make the Ghostty VT bridge compatible with both void and error-union ReadonlyStream.nextSlice return types
• verify the bridge against the latest Ghostty main head (fa10237), which matches what the macOS release workflow clones in CI
• keep the PR source-only and avoid committing rebuilt dylib artifacts

Verification

• zig build -Dghostty=/Users/hack/dev/hack-dance/hack-cli/apps/macos/vendor/ghostty -Doptimize=ReleaseSafe -Dtarget=aarch64-macos in apps/macos/Experiments/GhosttyVTBridge
• bun run macos:ghostty:bundle

Context

The release workflow already clones the latest Ghostty head during build-and-notarize, so the failure was caused by bridge API drift rather than an outdated vendored revision.

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Latest commit: 8c13dc0

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